I would not suggest eBay because 1) you won't know what kind of quality you'll get and 2) it's much cheaper to print your own at a local photo shop if you can find a good high resolution (non-copyrighted ;-) ) picture.

You can get photo printed off at a photo lab, or you could look on Ebay as people often sell blank postcards of celerities on there :)

Search for jpeg pictures online. And then print them out at:
http://www.nationsphotolab.com/home.asp

It's 25 cents for one 4x6 Kodak photo. If the jpeg is clear, then the photo is very clear. If you enlarge the jpeg, then you'll lose some resolutions.
Shipping is about 5 working days by Fed Ex. Printing is less than 24 hours.
If you order over $50, the shipping is free. If less than $50, shipping is $7.

I just placed an order and got the package last weekend. The quality and colors are top notch.

Good luck.

Can anyone tell me where is the cheapest place to buy good quality photos (preferably postcard size)? I am new to sending photos and I am in need of help. Or, if you could direct me to a link on the site that could help me, I would be very appreciative. Thanks.